Process of producing pulp and treatment of residual liquors



Patented Dec. 1 1931- Umrso STATES PATENT OFFICE 1.11m BRADLEY, or moNrcLAm, NEW JERSEY, aunnnwm 2. items, or mature BUB-G, NEW YORK, ASSIGNORS BRADLEY-MGKEEFE CORPORATION,

N. Y., a coaroaa'non' or new YORK raocr'zss or raonuome rm AND No Drawing. Application filed Kay 9,

This invention relates to a process for produping pulp and treating residual liquor.

More particularly the invention relates to a process comprising digestingwoo'd, etc., 15. by means of a cooking liquor supplied with a sulfite of sodium, and dlgesting' wood, etc, by means ofcooking liquor supplied with I sodium"sulphide,-some of the sodium content of residual liquor from one type of digest 1 ing treatment bein utilized in cooking liquor of another type 0 digesting treatment. According'to one embodiment of the invention, we digest wood (for 2 example, spruce or other coniferous or non coniferous 3 Wood) by means of acid cooking 1i uorsuppliedwith a sulfite of sodium, such igestion usually being carried out under conditions adapted to produce commercially bleachable chemical pulp;'and we digest wood (for exother wood} by means of alkaline cooking liquor supp ied with sodium hydroxide and sodiumsulfid (either with or without sodium sulfite being supplied theretq? 'usuall conducting such digestion un er con 'tions adapted to produce chemical pulp.

Residual liquor resulting ro'm the, acid digestion treatment is separated from theresulting fibrous material and is subsequently subjected to a concentrating treatment in any suitable manner, to remove water. The resulting residue is treated to decom ose organic, matter and to obtain some sodium sulfid including sulfur derived from a constituent of such residual liquor, Some of such sodium sulfid is subsequently employed in the alkaline cooking liquor referred to abover -Residu al liquor resulting from the alka-. line digesting treatment is separated from .the result in fibrous material and issubsequently sub ected to a concentrating treatment in :any suitable manner, to remove waterfand the resulting "residue is treated to decompose organic matter and to obtain some sodium carbonate including sodium derivedfrom a constituent of such residual liquor. ".aSome of such sodium carbonate-is utilized in roducing asulfite of and the 'latter' ls used in cooking liquor for the acid digestion treatment.

ample, poplar, beech, birch, maple, pine or TREATMENT or RESIDUAL motions 192s. Serial No. 276,501.

The following example will serve to illustrate how the invention may be carried out in practice, although the invention is not limited'to such example, various modificatlons thereof being permissible without departing from the spirit and scope of the invention.

For the alkaline digest' around 10,000 pounds, bone-dry asis, of poplar or other suitable wood, etc., ma charged into a suitable digester and-t ere. into may be charged a. suitable volume of aqueous cooking liquorcontaining around 1,700 pounds of sodium hydroxide (NaOI-I) more or less, and around 500 pounds of sodium sulfid (m s), more or less, and around 5.00 pounds of sodium sulfite (mason, more orless. q The cookingliquor may vary considerably in the amounts and proportions 'of ,suc chemicals and the volumethereof ma be anything suitable. The alkaline coo ing liquor may be formed and the cooking operation may be carried out 'in any suitable manner, such for example as described in our U.S. Patent No. 1,651,665, dated Decem: ber 6, 1927,' or in one or more of our copendin'g applications for Letters Patent, Serial- Nos. 57 ,953 and 57,954, filed September 22, 1925, and Serial No. 120,514, filed OF NEW YORK;

treatmen July 3, 1926. Upon completion of the digesting operation,- the resulting materials are discharged from the digester and the residual liquor is removed from the resultmg fibrous materialby any suitable means. It is advantageous to so conduct the digestionoperation that the fibres of the resulting Around 10,000 pounds (bone-dry basis) of.

so-called hardwood (e, g. poplar, blrch, maple, etc.) may b'e'charged intosuch-digester, and there may also charged 'theremto a suitable volume of aqueous. cooking liquor supplied with around 2,000 pounds-of sodium sulfite (calculated as Na SO more or less, and around 800 to 1,600 pounds excess S0 (i. e. that over the amount calculated as present in N a SO More or less than 2,000 pounds of sodium sulfite (as calculated above) may be supplied to such cookin liquor; and the ratio of free to combined S 2 may be suitably varied -and regulated. When it is desired to obtain relatively strong chemical pulp which contains fibres that are readily bleachable to produce relatively strong high white fibres, such that they are suitable for being supplied in relatively large amount or proportion producin high quality papers, in some cases it is a vantageous to have the cooking liquor of such com osition that it contains no excess SO yond the sodium bisulfite (NaHSO stage, preferably having both N a SO and NaHSO in such cooking liquor in suitable amount and ratio. The cooking operation can be carried out as described in a co-pending application for U. S. Letters Patent, Serial N 0. 665,224, filed September 27, 1923, or any other suitable procedure may be adopted. The cooking liquor may be produced in any suitable manner, such for example as described in a companion or copending application, Serial N 0. 664,640, filed September 24, 1923. Wood other than that specified, e. g. spruce, balsam, pine, etc., may be digested by means of such type of cooking liquor when a difierent fibrous material is desired.

Upon completion of the digesting operation, the resulting materials are discharged from the digester and the residual liquor is removed from the resulting fibrous material by any suitable means. It is advantageous to employ such a cooking liquor and to so conduct the digesting operation that the resulting pulp is largely made up of fibres which are relatively strong and yet readily bleachable, as indicated above, especially when digesting so-called hardwood.

The residual liquors from the acid digesting treatment and the alkaline digesting treatment, respectively, may be treated separately, if desired, and the residual liquor from the acid digesting treatment may or may not be neutralized or rendered alkaline to litmus prior to subjecting it to the concentrating treatment to remove water from it. It is advantageous, however, to treat the acid residual liquor so as to render it at least neutral, and preferably alkaline to litmus, e. g. by treatment thereof with a reactive alkaline sodium compound or compounds. Such treatment of the acid residual liquor may be used to regulate and control the proportion of sulfur present in sodium-bearing material resulting from decomposition of sodium-bearing organic matter by a furnacing treatment. For thus treating the acid residual liquor, reactive sodium-bearing material, such as that presentin residual liquor from the alkaline digesting treatment or in soda recovered or derived from residual liquor, e. g. sodium carbonate or sodium sulfid or sodium hydroxide or mixtures of two or more of these compounds may be used in the required amount or amounts. Thus the acid residual liquor may be treated by slowly and gradually adding thereto, while the liquor is maintained hbt (e. g. at or near the boiling point) and is being agitatedto remove released gas, e. g. CO the required amount of alkaline residual liquor to fix the free acidand provide a mixed liquor which has the desired degree of alkalinity (to litmus) such as to prevent its injuring iron parts of a multiple-effect evaporator at a point or points where the liquor comes in contact with it.

By proceeding in the manner outlined,-

sodium-organic compound of the alkaline residual liquor. Such precipitated matter may be removed from the liquor, in whole or in part, in any suitable manner, and such removed organic matter, etc., separately delivered into the furnace hereinafter referred to; or/and the mixed liquor may have added thereto a suitable sodium compound which is capable of redis'solving the precipitated organic matter then present. Thus some causticized soda liquor may be added thereto in the required amount, or some sodium carbonate-sodium sulfid liquor may be thus used, or both causticized and uncausticized soda liquor may be thus employed so as to redissolve such precipitated organic matter as may then be present. In this manner the mixed liquor can be made ready and suitable for introduction into a multiple-effect evaporator, the precipitated organic matter having been removed in Whole or in part and suitable alkali added to the liquor in such amount as will tend to minimize or preventorganic matter separating therefrom during treatment thereof in the evaporator, e. g. when such evaporator contains iron tubes. i

The mixed residual liquor, which may be prepared as above, is subjected to a concentrating treatment in a multiple-effect evaporator so as to obtain a concentrated mixed liquor, e. g. around 30 to 40 Baum, more or less, and the concentrated mixed liquor is subjected to a further treatment to remove remaining water therefrom and the resulting dry residue is suitably furnaced under reducing conditions so as to obtain a furnace prodsodium sulfid. The reducing furnace used I centrated liquor may be sprayedQor/and asses-2e uct which contains sodium carbonate and sodium sulfid. The ratio of these two compounds therein contained may vary somewhat depending upon the amounts and contents of the residualliquors which have been mixed together and upon the amount of sulfur carried away by the furnace gases, etc. By

' using a much larger amount of soda in the alkaline residual liquor than that in the acid residual liquor, i. e. the alkaline residual liquor added to the acid residual liquor con-- taining a much larger amount of soda than that contained in the acid residual liquor, the

furnace product derived therefrom usually contains a larger amount of sodium carbonate than of sodium sulfid, and the furnace gases may be similar to those customarily employed in mills which operate the conventional socalled sulfate process, or rotary incinerators of the soda process may be operated under reducing conditions.

The t'reatmentof theiconcentrated liquor from the evaporator may be carried out in 'any suitable manner, employing any-suitable equipment; but we have found that such conatomizedinto gases coming from the furnace, either directly from the furnace, or after passing auxiliary combustionfchamber (if any) operated in conjunction therewith, or

after such gases have been passed through a steam boiler (following the combustion chamber) andused for generating steam and for effecting a partial coolin of the gases Such sprayed or/and atomized liquor undergoes an additional concentration as a result of such treatment. The. mixed liquor, at suitable concentration, may be sprayed or/and atomizedinto the hot gases, as above indicated, and thereby converted into a substantially dry finely divided material which includes 'a substantial amount of sodiumorganic matter, e. g.- by atomizing highly con- -centratedresidual liquor or mixed residual liquor into such gases at around 200 to 400 I I. (more or less); The resulting gases, in-

cluding water vapor andsuspended matter, may be passed into a high voltage. electrical precipitatonso operated as to remove the sub stantially dry material from such gases,

allowing theresulting gases and water vapor to pass onward as pointed out ina co-pendm application, Serial- No. 267,047, J filed 'Ap 3rd, 1928. In this way a-substantially material. is recovered from thegases.

Such dry material may thereafter be subj ected to a reducing furnacing treatment, for example as disclosed in said co-pending application,-thus producing a non-gaseous furnace product which includes sodium carbonate and sodium sulfid and also producing a gaseous product including-sulfur-bearing material. By introducing a regulated amount of air into the auxiliary com ustion chamber, the sulfur-bearing material of the gases is present mostly, if not all, in the form of oxy-sulfur material, e. g. S or/and S0 or a compound or compounds-including such material or/and materials ('e. g. Na SO When the resulting gases are treated as pointed out above, a large part of the oxy-sulfur bearin material ,(e. g."Na SO is removed from the gases along with the substantially dry finely divided material described above. By suitably regulating the amount of air supplied to'the combustion chamber, the gases may carry a considerable amount of sulfur dioxide. 1 I q The gases which pass on from the spray chamber or chambers may contain sulfur d1.- oxide which may be removed therefrom,e1 g. by scrubbing such gases at a point or points.

beyond the spray cham er or chambers and electrical precipitator (if any), referred to above, by means of suitable liquor, e. g. an aqueous solution comprising sodium carbonate or/and sodium sulfite, for instance soda liquor derived from the furnace product which has been treated to remove or eliminate sulfid-sulfur or to convert sodium sulfid thereof directly or indirectly into sodium sul- Thus a solution of. the sodium compounds from the reducing furnacing operation may be treated to remove sulfid-sulfur therefrom, or/and to convert sodium sulfid directly or indirectly into sodium sulfite by a regulated oxidation treatment, such for example as described hereinafter or in copending applications for U. S. Letters Pat- 7 ent, Serial No. 686,137, filed January 14, 1924; Serial No. 248,960, filed January 23, 1928 and Serial No. -267,476,'filed April 4th, 1928.

' Such a resulting-solution may be used to scrub such gase to regain sulfur dioxide therefrom. The resulting solution, following the scrubbing operation, may be further sulfited, to such extent as needed or desired, and/or ma"; be otherwise treated to prepare it for use in a digesting operation, e. g. one employing a sulfite of sodium type of cockin liquor.

e have found that the ratio of sodium sulfid to sodium carbonate in the reduced furnace product, referred to above, depends in part upon the ratio of sulfur to soda in the material which is charged into the reducing furnace and upon the amount of sulfur-bearing material removed by'furnace gases; and, furthermore, upon the composition of the sul- Serial No. 266,863, filed April 2, 1928,

4 Ill fur-bearing material in the material charged into the furnace. Thus, for a given ratio of sulfur to soda, in the charged material,-it is desirable to have the included sulfur-bearing material contain a relatively large amount of an oxy-sulfur compound of sodium. Sodium sulfate appears to be more advantageous in n the charge than sodium sulfite for the same total sulfur and soda contents in the charged material, as it seems to retain the sulfur with the soda more effectively, and thus provides a relatively higher sodium sulfid content in the reduced furnace product. Accordingly, by using an auxiliary combustion chamber into which a regulated amount of air is introduced, sulfur-bearing material in the gases may be converted, to a considerable extent, at least, into a sulfate condition, although by regulating the conditions, especially the air supply and the temperatures, the gases may also carry a considerable amount of S0 After spraying concentrated residual liquor from a digesting operation into the gases, 0. g. at a point or points beyond the steam boiler Where the hot products of combustion have been used to produce steam, and after using an electrical precipitator to remove from warm gases resulting suspended solids in a relatively or substantially dry condition, the warm gases which pass beyond such precipitator may contain a sufficient amount of sulfur dioxide to justify scrubbing or other wise treating them to regain sulfur dioxide. The amount of sulfur dioxide which may be present in such gases depends upon the conditions. For instance, if the material charged into the reducing furnace (e. g. a conventional smelting furnace) has a high content of sulfur as compared to soda, in a compound or compounds, such for instance as a sulfite of sodium or/and sulfo-or'ganic matter, and also if the concentrated residual liq uor, sprayed or/and atomized into the furnace gases at a point beyond the boiler, contains a relatively large amount of such sulfits ,etc., such as residual liquor from the acid digesting operation described herein usually contains, the gases which are to be scrubbed may contain. a very considerable amount of sulfur dioxide.

In operating a multiple-liquor mill according to the present process, it is advan tageous to regu'latethe reducing furnacing treatment and the oxidizing treatment of the gases so that the gases beyond the combustion chamber contain considerable amounts of both sulfate and sulfite sulfur, and to remove from such gases substantially all of the sulfate sulfur,.e. g. by spraying or/and atomizing residual liquor thereinto and removing a concentrated material, as pointed out above, and to leave in the gases a considerable amount of sulfur dioxide and to subsequently treat such gases to regain the sulfur dioxide and form a sulfite of sodium,

and to employ such sulfite of sodium in a cooking liquor of the sulfite of sodium type. The furnace gases, after having passed through a suitable cooling means, for example, a steam boiler, may with advantage be passed through an electrical precipitator so operated as to remove from the gases the suspended solids such as sulfate of sodium, and to allow the S0 to pass beyond. After the gaseshave been substantially freed from sodium sulfate and additional sulfate radical, if any, the residual sulfur dioxide-bearing gases are treated by means of sodium carbonate-sodium sulfite material, in solution, so as to regain such sulfur dioxide and to convert sodium carbonate into sodium sulfite. The latter sulfited soda-bearing mate rial may be further adjusted or modified, as needed or desired, to prepare it for use in a cooking liquor of a sulfite of sodium type, etc.

The sulfate sulfur removed from such gases is later charged into the reducing furnace. Inthis method, the sulfate sulfur is utilized in an advantageous manner to provide a reduced furnace product of relatively high sodium sulfid content, which can, if desired, be advantageously employed in the alkaline cooking liquor of the process, and sullite sulfur is regained from the gases and is employed, at least in part, in the sulfite of sodium type of cooking liquor, That is to say, we have found it de sirable to conduct the recovery operations in such a manner as to provide a relatively high content of sodium sulfate in the material which is charged into the reducing furnace, some of such sulfate sulfur having been removed from gases uor, or it can be added to the material which" is to be charged into the reducing furnace, or it can be added to the material within such furnace. Thus sodium sulfate can be used to replace soda losses and also to supply some sulfur to the cycle, sodium sullid being derived therefrom by a reducing treatment in the presence of incandescent carbon.

When the amount of residual liquor available from the alkaline type of digesting operation is suflicient, a portion of such residual liquor can be subjected to a suitable furnacing treatment (e. g. in a rotary incinerator) Without having any other sulfur-bearing material added thereto. The furnace product which may be thus obtained, especially if the soda material has been given an oxidizing treatment, usually carries a relatively large amount of sodium carbonate as compared with sodium suliid. lVhen the amount of sodium sultid in such furnace product is sufficiently low, an aqueous solution of the liquor of the present process.

soda thus recovered can be directly sulfited in any suitable manner to form cooking liquor for -the sulfite of sodiumtype of digestion, i. e. an acid sulfite of sodium cooking Such aqueous solution of the recovered soda may advantageously be used to regain sulfur dioxide from the furnace gases of either one or both of the above mentioned furnacing operations, such as by the method pointed out above.

The portion of alkaline residual liquor which is to be subjectedto such a separate furnacing treatment, if any, which may be carried out in a conventional rotary incinerator, may be subjected to an evaporating treatment and may then be directly charged into a furnace of any suitable type, or it may be subjected to a spraying or/and an atomizing treatment, in the manner pointed out, by

means of gaseswhich carry little or no sulfur-bearing material and the resulting con-' centrated material may be recovered and thereafter be charged into a suitable furnace such as pointed out above or into any other suitable furnace. Such portion of the concentrate'd alkalinen'residual liquor may be treated in themanner and with the equipment used in the so-called Soda Process.

- If desired,-sodium carbonate can be added, to the aqueoussolution of the soda recovered in the furnace product which is to be sulfited,

thereby replacing some of the soda losses; ale though when enough sulfate of sodium has been added to'the material which is to undergo the-reducing furnace treatment, previously described, such addition of sodium carbonate can be dispensed with to advantage. Y

Owing to the fact that sulfate of sodium supplies sulfur as well as soda to the cycle a relativelv small amount of additional su1 fur is needed tojreplacelosses thereof. This may be supplied in any suitable manner,

e. g. bv burning. sulfur in a sulfur-burner to provide S0 and this maybe used to form a sulfite. of sodium or/and to increase the.

sulfite content of the solution which is to be utilized in preparation of the cooking liquor of the acid type. By operating according to. the methods outlined above. in which a largeamount of sulfur isregained in useful condition. the amount of such newly supplied sulfited to form a 'sulfite of sodium type of sulfur to be' thus added is relatively small. In case the aqueous solution'which is to be cooking liquor e. g. the-acid cooking liquor de cribed above, contains such. an amount of sodium sulfid'as to renderjit objectionable or unsuitable for. a direct sulfitjng operation in which SO gas is introduced into a'cold solution containing such an amount of sodium j sulfid, the aqueous solution may be given a preliminary titeatment prior to sulfiting it,

.e.flg. by means" ofsulfur-dioxide gas. In co-' pendinglapplications we have described various met ods of treating such an aqueous solution in order to obtain suitable sulfite of sodium cooking liquors, e. g. of the acid type. One or more of such methods, or any other suitable method for treating such aqueous solutions to obtain suitable acid cooking liqnor, may be employed, and the resulting cooking liquor used in a digesting operation.

Such a solution may. be treated with an amount of zinc sulfite, or of zinc om'de, or

advantageously of sodium zincate, such as sulfid to form insoluble zinc sulfid so asto remove substantially all sulfid-sulfur from the solution. The treated solution is thereafter separated from the precipitate by any suitable means and the solution is thereafter subjected to such further sulfiting treatment as desired or needed.

will react with substantially all of the sodium Alternately, sodium sulfid in such an.

aqueous solution may be treated with a suitcharged into the reducing typeof furnace,

the resulting furnace product may be admixed'with water and agitated and heated, if

needed, and the resulting solution may be separated from the resulting iron sulfid by A relatively insoluble alkaline-earth metal compound or compounds may be supplied to the mixture andit may be removed from the solution along with the iron sulfid so as to aid in separating a clear liquor. Thus basic magnesium carbonate in suitable amount ma any suitable means and in any suitable way.

be so used, or other magnesium compoun s may be used to clarify the liquor as described a in our copending applications Serial Nos. 686.137 filed January 14. 1924', 704,176 filed The solids removed from the liquor, e. g. a mixture of iron sulfid and the alkaline-earth metal compound or compounds. may be returned to the' reducing furnace for treatment along with sodium-organic matter and su1- fur-bearing material. The furnacingoperation of the mixed charge should be soconductedand regulated that sulfur of the iron sulfid is driven out from its combination with the iron. e. g. into the furnace gases so asto'provide oxy-sulfur-material in the April 4, 1924, and 713257 filed May 14, 1924..

gases bevond the combustion chamber, Such oxyrsulfur material can be. regained from the furnace gases in a manner pointed out above. Instead of treating the iron sulfid precipitate, etc.. along with anotherlot of sodium-or ani matter,e. .g. in the manneroutlined a ve,

such. precipitate, may be given a separate treatment in another furnace under conditions adapted to form an iron compound (e. g. sodium ferrite) which is suitable for ad dition to the aqueous solution of the recovered sodium compounds and for reacting with sodium sulfid thereof to form iron sulfid. In this way the sulfid-sulfur in the solution may be reduced to a suitable amount or it may be substantially eliminated therefrom.

Sodium carbonate-sodium sulfid solution may be treated with a suitable sulfate or sulfates so as to convert any desired portion or substantially all of the sodium content of the sodium sulfid and sodium carbonate into sodiumsulfate and under conditions adapted to remove sulfid-sulfur from the solution; then the sulfid-free (or substantially sulfid free) solution may be thereafter treated in any suitable manner so as to convert sodium sulfate of the solution into a sulfite of sodium. Thus the sodium carbonate-sodium sulfid liquor may be treated with ammonium sulfate or/and magnesium sulfate, or with calcium sulfate and magnesium sulfate or/and ammonium sulfate. Thus calcium sulfate may be used to react upon a portion or all of the sodium carbonate and the other sulfate or sulfates maybe used to react upon the sodium sulfid, and the solution may be heated (e. g. boiled) to remove therefrom. substantially all liberated H S. The latter may be thereafter burned to form SO which may be used to form a sulfite for use in a cooking liquor. The precipitated material, if any, may be removed from the solution before it is treated with the sulfite radical. The sodium sulfate of the solution may be thereafter treated with calcium sulfite and excess S02 in amounts regulated so that calcium sulfate is formedv as a precipitate, thus removing from solution substantially all of the sulfate radical, and the sodium content of the sodium sulfate is converted into an acid sulfite of sodium in the solution. The acid solution is thereafter separated from the precipitate and is then available as a cooking liquor or for preparation of cooking liquor.

All of the alkaline residual liquor, or any desired or necessary portion of it, may be admixed with the acid residual liquor and the resulting mixed liquor treated as indicated above; or the two types of residual liquors maybe treated separately so as to regain the soda in separate furnace products. The two types of residual liquors may thus be separately treated by the spray evaporation treatment to form substantially dry materials.

These materials may be admixed in any desired ratio. to form a mixture and the latter may be subjected to a furnacing treatment. By regulating the amount of alkaline residual liquor admixed with acid residual liquor, and the ratio of soda to sulfur in the material charged into the reducing type of furnace, the ratio of sodium carbonate to sodium sulfid can be regulated so as to give a regulated scribed in our copending application lime so as to provide the alkaline cooking liquor in desired amount, and another portion of it may be treated to remove sulfidsulfur or/and to produce sodium sulfite including sodium content of such sodium sulfid. Such latter portion may be further treated so as to produce the acid cooking liquor for use in the process of the present invention.

A portion of the sodium carbonate-sodium sulfid solution, e. g. sufficient to provide the desired amount of sulfite of sodium which is to be employed in the acid cooking liquor,

may be treated with sulfur dioxide bearingmaterial while maintained at around the boiling point, in a suitable vessel such as a tank provided with an agitator as more fullsy deerial No. 267 ,47 6 filed April 4, 1928. Sulfur dioxide bearing gases, for example those obtained from the combustion chamber of a sulfur burner of the conventional type, may be gradually and slowly introduced into such solution at a point or points near the bottom of the tank in such manner and amount as to react with the sodium sulfid to drive out hydrogen sulfid from the solution and to convert most or substantially all of the sodium sulfid into either, a carbonate of sodium or/and a sulfite of sodium without forming any large amount of sodium thiosulfate. The hydrogen sulfid removed from the solution can be delivered into a combustion chamber of a sulfur burner and therein burned to sulfur dioxide and the sulfite regained for reuse in cooking liquor; or such hydrogen sulfid can be delivered into a combustion chamber operated in conjunction with the reducing furnace into which sodium-organic material is charged, the hydrogen sulfid being thereby "oxidized to an oxy-sulfur compound or comiao mixed liquor moderately alkaline to litmus, then mixing the resulting moderately alkaline residual liquor with the residual liquor from the alkaline digesting treatment, and charging this mixture of residual liquors into a make a strong solution which contains sodi- ,um carbonate and sodium sulfid, and this latter solution may be divided into two or more parts. One of such parts can'be causticized by means of lime to provide the alkaline cooking liquor (comprising sodium hy-.

droxide and sodium sulfid, with or without sodium sulfite, etc.), and another of such parts may be directly sulfited at or around the boiling point, in a tank provided with an agitator, by means of available sulfur dioxide in amount suflicient to convert at least one-halfand preferably more than one-half of the sodium sulfid directly into sodium sulfite. The hydrogen sulfid liberated and removed from the liquor maybe delivered into a combustion chamber and therein burned to form sulfur dioxide or/and trioxide. Thus sulfur dioxide gas, which maybe supplied in any suitable manner (for example as warm or hot sulfur-burner gases), may .be introducedinto the sodium carbonate-sodium sulfid liquor in amount sulficient and under conditions regulated so as to convert the desired ment is advantageously driven out from the solution substantially as fast as it is formed and such H S may with advantage be introduced into a combustion chamber 0 rated in connection with the furnace in whic the sodium organic compounds .are decomposed to form the sodium carbonate and the sodium sulfid. In such combustion chamber the hy drogen sulfid is readily oxidized by oxygen of the gases and the resulting oxy-sulfur compound or compounds may with advantage be recovered from the resulting gases in a manner heretofore pointed out.

The sulfiting of the liquor maybe terminated at. any suitable time after the sodium sulfid has been decomposed and the hydrogen sulfid; removed from the liquor with substantial cdmpleten'ess', or the sulfiting treatmentf ma be continued until the liquor containsa ratio of combined to uncombined SO rendering it suitable for the acid sulfite of sodium type of digesting treatment of the process.

By thus effecting the sulfiting of a portion of the sodium carbonate-sodium sulfid liquor at the boiling point of the liquor and while it is being vigorously agitated, the sulfite of pared in. a simple and advantageous manner, thus permitting of a simple method of treat ing the residual liquors from both types of digesting operations, and the recovered soda can be divided into such portions as may be desirable in'the process.

The strength of the sodium carbonatesodium type of cooking liquor can be presodium sulfid liquor may be anything suitable, but it is of advantage to hav'e the solution of such strength that the respective cooking liquors can be produced without subjecting the liquor to an additional evaporating operation. That portion of the sodium carbonate-sodium sulfid liquor which is to be sulfited, e. g. by free sulfur dioxide (and which may advantageously be supplied as sulfur burner gases from a point beyond the combustion chamber so as to avoid the presence of elementary sulfur in the gases), is usually at a relatively high concentration so as to avoid having any' very large amount of hydrogen sulfid present in the liquor at any time. Such solution may,for' example, con tain around 1 50 to 200 grams'per litre more or less, of 's odiumcarbonate (Na CO and around 50 to 100 grams per litre, more or less, of sodium sulfid (Na-3S), and solutions which are almost saturated'with such sodium compounds may be used, if desired, thereby reducing the amount of water present. When hot sulfur burner gases of the type described are employed for the hot sulfiting treatment,

some of the water of the solution may be evaporated thereby, thus producing a liquor of increased concentration for precipitating out a compound of sodium, as the case may be. After completion of the sulfiting treatment, the liquor can be treated to prepare it liquor is first treated with the available sulfur dioxide, e. g. by delivering SO gas into the liquor at a relatively slow rate and agitating the boiling liquor, little if any H S comes from the liquor. After a sufiicient amount of SO has been absorbed, the H S is discharged from the liquor at anincreasing rate until amaximumrate is reached. The Ins continuesto come from ,the liquonin copious amounts until a large portion of the sodium sulfid has been reacted upon, after which the rate at which the H S comes from the liquor decreases and finally substantially ceases to come from the liquor. At such time, the sulfur dioxide may be shut off from the tank and the tank may be continued under boiling conditions and the agitation continued to drive out some more H S which is then coming from the liquor at only a 'slow rate. After such continued treatment for a period of around a half-hour or so, the liquor may be given a further sulfiting, if desired, to increase the amount of sulfite radicle therein and so as to obtain any desired ratio of c0mbined to uncombined S0 Such additional sulfiting, after removal of the hydrogen sulfid, may be effected in any suitable manner. For example, such resulting liquor (containing sodium white and usually containing some sodium carbonate) may be used to scrub gases from the furnacing operation to regain sulfur dioxide therefrom, when such gases contain sulfur dioxide in amount such as to justify it; or the liquor may be sulfited in any other suitable manner and to any suitable degree.

The concentration of H S in the gases removed from the tank in which the sodium carbonate-sodium sulfid liquor is sulfited while "boiling, will vary considerably depending upon conditions. When a rich SO gas I (such for example as when SO from burner gases is absorbed in water or in a sodium sulfite solution and the free S0 is later driven out therefrom)-is used for the sulfiting of the sodium sulfid, the gases will usually be much richer in H S than when burner gases are directly used for the treatment of the sodium sulfid. The rich H S gases may be burned in a combustion chamber operated in connection with a sulfur burner, thus increasing the amount of SO in the gases. Diluted ILS gases may be delivered into such a combustion chamber or they may be delivered into the combustion chamber of the furnace in which the sodium organic matter is decomposed.

Alternately' the H S may be admixed with a suitable amount of air or/and S0 andthe m-ixed gases passed through a bed of suitably heated iron oxide or ferruginous bauxite under conditions regulated to selectively oxidize the hydrogen to form water vapor and to leave the sulfur in the form of elementary sulfur. The latter may be recovered in molten condition in a manner well-known for the treatmentof hydrogen sulfid.

In another method, the hydrogen sulfid, especially the dilute gases, may be scrubbed with a suitable solution of sodium carbonate to form'a solution which contains both sodium acid carbonate and sodium ,acid sulfid (NaHCO and NaHS) and the resulting solution may be subjected to a suitable aerating treatment to selectively oxidize the hydrogen to form water and to set free the elementary sulfur which can be removed from the resulting liquor in a manner understood. Such a method of treating dilute hydrogen sulfid gases has been described in connection with purification of illuminating and fuel gas.

When the hydrogen sulfid is delivered into a combustion chamber used in conjunction with a sulfur burner and when sulfur burner gases are used to treat the sodium sulfid in the li uor, the hydrogen sulfid may be delivered into a' separate combustion chamber supplied with the portion of sulfur burner gases which i not used for treatment of the sodium sulfid, and another combustion chamber is used for producing the gases which are to be used for thetreatment of the sodium sulfid. In this way building up of nitrogen, etc. to an objectionable point is largely obviated, although sulfur burner gases and combustion chambers are used. The sulfur dioxide-bearing gases are used in part for one treatment and in part may be used for further sulfiting of the partially sulfited liquor from the other treatment.

Then a steam boiler is used in the manner indicated above to utilize heat from the furnace gases, the steam therefrom may be used in a multiple-effect evaporator to concentrate residual liquor, or/and in a digester in which wood is cooked by a cooking liquor of the present process.

In accordance with the present invention, a furnace product is obtained, e. g. by one of the methods heretofore outlined, which contains sodium carbonate and a relatively large amount of sodium sulfid. Such a furnace product may be obtained by mixing with the acid residual liquor just enough, or moderately more alkaline residual liquor than is re-.

quired, to fix any free acid contained in the acid residual liquor, then subjecting the neutral or alkaline mixed liquor to a concentrating treatment including a spray evaporation treatment by means of furnace gases coming from a reducing furnace in which sodiumorganic and sulfur-bearing materials are treated, such furnace gases preferably containing a considerable amount of sulfate sulfur, and recovering the resulting dried material by means of an electrical precipitator; then subjecting such dried material to a burning and reducing treatment in the furnace under conditions adapted to obtain the clesired furnace product. Some of the sulfur content of the material charged into the fur nace is usually eliminated into the furnace gases by such a furnacing treatment and the furnace product as obtained usually contains a considerable amount of sodium carbonate as Well as sodium sulfid, the amount of sodium carbonate usuallybeing larger than that of sodium sulfid. The furnace product is I treated with water to obtain a strong solution comprising sodium carbonate and sodium sulfid.

This solution may be cooled and thereafter directly sulfited by means of cool SO to form a relatively large amount of sodium thiosulfate therein, but leaving some of the sodium carbonate in such sulfited liquor. The sulfiting may thus be carried out under such conditions as to avoid driving out any considerable amount of sulfid-sulfur as hydrogen sulfid, it being preferable in this embodiment of the invention to retain all of the sulfur in the solution so as to obtain the maximum amount of thiosulfate. The sulfiting should usually be terminated when substantially all of the sulfid has been acted upon, although a small to moderate amount of sodium sulfite can be produced therein provided the re-' left in era'ble amount of sodium carbonate and may contain some sodium .sulfite, is thereafter subjected to a regulated oxidizing treatment under conditions adapted to convert the sodium thiosulfate into sodium sulfite, some of the sulfur content of the thiosulfatebeing oxidized to sulfite and allowed to react with available soda to form sodium sulfite. Thus the sodium carbonatemay be, at least in part, converted into sodium sulfite by means of the regulated oxidation of the thiosulfate, although the partially sulfited liquor may be given a regulated causticizing treatment, e. by means of lime, to convert a preponderating portion of the sodium carbonate into sodium hydroxide, prior to the'regulated oxidation treatment to convert thiosulfate into sulfite. In case such a causticized liquor is I i lime mud may be removed from the causticized liquor which contains the thiosulfate), may be effected in any suitable manner. For example, it may be treated to remove water therefrom to form a relatively dry finely divided soda-bearing material which includes thiosulfate and sodium carbonate or/and sodium hydroxide. Such material ma have other suitable and finely divided soli mate uted throughout it w ile it is being thus oxidized.- Such finely divided material may be treated by means of air or other oxygen-bearmg gases at a temperature ranging from around 100 (3., up to around 160 (3., more or less usually around 120 to 140 C., so as to subject the finely divided material to suitable contact with a regulated and sufficient amount of oxygen to oxidize loosely combined sulfur of the thiosulfate to sulfite, and under conditions such that the formed sulfite radical may react with sodium carbonate or/and sodium hydroxide to form sodium sulfite.

The air or other oxygen-bearing gases for such treatment may be suitably heated to the desired point in any suitable manner and the oxygen-bearing gases may be caused to pass countercurrent to the soda-bearing material; or such gases and the'soda-bearing material may be brought into intimate contact in any other suitable manner. Thus the material in suitably finely divided condition may be blown into, or the concentrated solution may be atomized into, the warm oxygen-bearing gases and allowed to react therewith to the desired extent and -the treated solids, may thereafter be removed from the residual gases by means of an electrical precipitator, for example. Or the suitably prepared soda-bearing material may be charged into a, suitable furnace, such for example as a multiplehearth furnace, and therein subjected to a progressive oxidation by means of such heat ed air brought into the lower part of such a oxidation at suitable temperature as it travels from the charging end to the discharge end. Upon completion of the oxidation of the thiosulfate to the desired degree, as indicated above, the resulting soda-bearing material may be dissolved in water in suitable amount and the resulting solution may be given such further sulfiting or other treatment as may be needed or desired to prepare the same for use in cooking liquor either for the acid type or for the alkaline type of digestion, or,for both types. In the above embodiment of the invention, it is desirable to retain a relatively large amount of sulfur in the furnace product as sodium sulfide, and to usesuch material in forming a'sulfite of sodium as pointed out. .The ratio of sodium hydroxide to sodium sulfid in the alkaline cooking liquor may be adjusted and controlled by mixing with H -uor which is high in sodium sulfid aregulate d amount of liquor which is relatively high in sodium carbonate and low in sodium sulfid,

such as may be obtained by a furnacing treatment of a regulated portion of the alkaline residual liquor from the alkaline digesting operation, in a separate furnace, and without adding thereto any additional sulfur-bearing material. Thus in accordance with this embodiment of the invention, the sulfur content of the sodium sulfid is used, at least to a considerable extent, in forming a sulfite of sodium and care is taken to avoid driving out sulfid-sulfur from the solution thereof as hydrogen sulfid.

Yes

In some cases, the treatment of sodium carbonate-sodium sulfid solution may be carried out with a combined sulfiting and oxidizing treatment. Thus the concentrated soda solution may be caused to pass countercurrent to gases from a sulfur burner of such compositionthat they contain nitrogen, sulfur dioxide and a considerable amount of oxygen. Such ases may be cooled in any suitable manner, i needed, so that they are around 140 to 150 C., more or less, when they are brought into contact with a relatively dry and finely divided soda-bearing material. The oxygen of the gases serves to oxidize thiosulfate sulfur to sulfite sulfur, and the sulfur dioxide of .the gases serves to sulfite some of the sodium carbonate to form an oxy-sulfur compound of sodium. By regulating the composition, amount and temperature of such burner gases and regulating the composition and rate of ..flow of the concentrated soda-bearing solution, andby adequate agitation and time for.

available sulfur to be oxidized to sulfite sulfur to the desired degree, the soda-bearing material removed from the discharge end of .ghe a paratus, in which the treatment is efecte may carry a relatively large amount of sod1um sulfite and little if any thiosulfate. Such discharged material may be further sulfited or otherwise modified as needed or desired to prepare it for use in producing a type of cooking liquor described above.

The following equations will serve to further illustrate various steps of treating sodium sulfid to produce sodium sulfite by means of a regulated oxidation treatment at suitable temperatures' as herein described.

4Na2CO3 2Na S 3NagSgOa 315111 008 C 2 41-120 The furnace product obtained as a result of the reducing furnace treatment, which contains sodium carbonate and sodium sulfid and usually with the former in preponderating amount, such for example as described above, may be 'treated with a limited amount of water so as to obtain a hot and highly concentrated solution of such sodium compounds. Such solution can be sprayed or atomized into a spray chamber and. therein subjected to the evaporating action of hot gases which contain a limited amount of oxygen, so as to obtain a relatively dry and finely divided soda-bearing material, and the resulting suspended matter can .be removed from the moisture la'den gases by passing the mixture into a suitable electrical precipitator which is preferably operated at a temperature above the dewpoint of the moisture laden gases, the

' gases and contained moisture being allowed to pass beyond the precipitator. Such finely divided and relatively dry or substantially dry soda-bearing material may thereafter be blown, for example, into a flue or chamber which is also supplied with heated air at a temperature ranging between 100 and 160" C more or less, the usual temperature of such gases ranging advantageously between 120and 140 6. The heated air may also *have a small or moderate amount of steam therein to facilitate carrying out the oxidation treatment. The finely divided material is thus brought into a highly disperse condition, in suspension in the gases, and excellent opportunity given for bringing the sodium sulfid and the oxygen into contact so as to cause an oxidation of the sulfid-sulfur to form sulfite-sulfur, and-the amount ofoxygen allowed to react with sodium sulfid can be suitably regulated by controlling the amount of air and the amount of sodium sulfid. Y

The oxidizing chamber is made of adequate size to permit the desired degree of oxidation being effected before the solids are removed from the The treatment 15 further improved gases and suspended matter into an electrical precipitator and using a high voltage field between the electrodes to precipitate the to the desired degree, the oxidationis terminated so as to avoid producing an excessive amount of sodium sulfate such as might otherwise occur if the oxidation treatment were continued for too long a time. By

ases. ivy bringing the residual using an electrical precipitator afterthe oxidation chamber into which the sodium sulfid,

etc. is introduced,the oxidized material can be promptly effectively removed, thus tained. Thus the hot and concentrated sodiumcarbonate-sodium sulfid solution described above can be sprayed into hot oxygenbearing gases under conditions to remove the desired portion of the moisture and a relatively dry material may thereby be oxidized to the desired degree. The oxidized material is then removed from the moisture laden gass-in any suitable manner and by any suitable means, an advantageous means being, for

example, an electrical precipitator.

By usinga preponderating amount of sodium' carbonate along with the sodium sulfid, the sodium sulfid is brought into a different condition for the oxidizing treatment thereof than when the sodium sulfid is in -fid material is to be directly subjected; to a regulated oxidation treatment in a manner indicatedabove, there is the possibility that some of the sodium sulfid may be either un "deroxidized or overoxidized, e. g. into sodium sulfate, since it is usually preferable to overoxidize rather than to underoxidize and.

it is difiicult in practice to control the oxidation so closely that only sodium sulfiteis formed and yet-oxidize all of the sodium sulfid.

4 We have found that the amount of sodium sulfate formed in such an oxidation treat- -ment can be regulated to better advantage when the furnace product contains more sodium present as sodium carbonate than is present as sodium sulfid. Such a furnace product is readily obtained by treating the residual liquor in such manner that the ex- 'cess sulfur is driven off in the furnace gases.

, fite is employed to regain sulfur dioxide from the furnace gases, thus forming more sodium sulfite. By thus limiting and regulating the prggortion of sodium sulfid in the furnace pr uct and providing-furnace gases which contain a relatively lar e amount of sulfur dioxide, the soda and t e sulfur contents of the residual liquor can be in rather large part, at least, regaincdin .th'f'orm of sodium sulfiteand without havin for-med toomuch sodium sulfateor/and s ium thiosulfate.

The residual liquor from the sulfite of sodium type of digestion, whether'acid, neutral or alkaline (alt ough' any such acid residual liquor is customarily neutralized or/and rendered alkaline to litmus, as stated above, prior to introducing it into the multiple-effect evaporator) is subjected to a regulated concentrating treatment in a multiple-effect evaporator, after which the concentrated liquor ma ess or-the conventional sulfate process (socalled), under regulated reducing conditions, but with suflicient air being introduced into the furnace or furnaces so as to insure providing the kind of furnace gases described above (i. e. carrying such an amount of sulfur dioxide,'etc.) and to provide a furnace product which carriesmore sodium present as sodium carbonate than as sodium sulfid, as pointed out. The melt from a sulfate process smelter, for example, may be treated with a small to moderate amount of water and the treatment continued under such conditions as will convert a pr'eponderating amount of the sodium sulfid into sodium sulfite, usually oxidizing all or substantially all of the sodium sulfid either to sodium sulfite alone or in lessor part to sodium sulfate, and the resulting oxidized soda-bearing material may be used to regain sulfur dioxide from the furnace gases as described above.

If the recovery operation and equipment of the soda process are used, instead of those of the sulfate process, the furnac ing is neverthless carried out so as to obtain sodium sulfid and sodium carbonate, the

sodium content of the later compound usu- V ally and advantageously being larger in amount than that of the former compound, and the furnace gases are provided with a relatively large amount of sulfur dioxide which may be regained therefrom by the soda-bearing material resulting from the regulated oxidation treatment of sodium sulfid referred to above. With the recovery operation of the soda process, as well as with that of the sulfate process, it is advantageous to remove and regain substantially all of the sulfate radical from the furnace gases rior to treating them with the oxidized sodaaring material to regain sulfur dioxide therefrom. v

The black ash formed when concentrated be treated in the recovery apparatus 0 either the conventional soda procresidual liquor, such as described above, is 7 sulfid with a regulated amount of moisture,

or the materialmay be otherwise treated with water for such purpose. Forexample, the black ash may be admixed with a small amount of water and agitated or, ground der conditions which leave the material fine- .ly divided. This finel divided material may then be thoroughly ad mixed with air of suitabletemperature and in suitable amount to oxidize sodium sulfid thereof to sodium sulfite to the desired extent. Alternately, instead of treating the black ash in the foregoing manner, it may be finely ground in a relatively dry condition, either in the presence or absence of steam in regulated amount, and this finely ground relatively dry material may be subjected to the regulated oxidationtreatment by means of the oxygen-bearing gases, such as air at suitable temperature, and which may also'be supplied with a s mall to moderate amount of steam, either by drawing air through the mixture of carbon and the sodium compounds, or b rial, or by blowing such soda-bearing material into a chamber intowhich a suitable amount of air at suitable temperature is introduced, and the'resulting oxidized material may be regained from residual gases in any sultable manner and by any suitable means. Such an intimate admixture of carbon and sodium compounds includingsodium sulfid is advantageous, as it provides a relatively large surface to the air, etc-., and facilitates oxidation thereof under suitably controlled and regulated conditions.

The process can also be used in pulp mills in which combinations of different liquors are used other than that described above, for example, mixed liquors containing sulfur compounds can be dried and furnaced as set forth herein, and the'furnace product containing sodium carbonate'and sodium sulfid treated with the sulfite radical to form a mixture of sodium carbonate and sodium thiosulfate. A portion of this liquor can be causticized and treated to form a cooking liquor containing sodium thiosu'lfate and caustic soda such as is described in our co-pending applications Serial No. 713,257, filed May 14, 1924,;and Serial No. 705,711, filed April 10, 1924, and another portion subjected to a regulated oxidizing and treated;

to form a liquor containing a sulfite of sodium with or without some remaining thiosulfate. Liquors of these two types may be used in the cooking of wood and the resulting residual liquors mixed and regenerated accord ing to the present invention In some cases it may be found desirable to causticiz'e sodium carbonate remaining in the thiosulfate containing liquor. A portion of this causticized liquor may be used directly to form a cooking liquor and another portion then'subjected to a regulated oxidizing to form a cooking liquor containing a sulfite of sodium or sov dium sulfite and caustic sodaas-set forth in agitating a. mixture of air and such sodaearing mate-' The present application is a continuation in part of our co-pending applications Serial Nos. 133,239; 133,291, and 133,292 filed September 2, 1926, Serial No. 248,96O filed January 23, 1928, as well as the ap lications referred to in the foregoing speci cation.

We claim 1. The cyclicprocess of producing pulp from wood, etc., which comprises digesting one lot of such fibrous material in a liquor containing a sulfite of sodium, digesting another'lot of fibrous material in a liquor containing sodium hydroxide, separating a residual llquor from resultin fibrous material from each of such di estmg treatments, removing water from suc residual liquors, decomposing sodium or anic compounds of both residual liquors lrnacing them together, thereby producing a furnace product comprlsing sodium carbonate and sodium sulfid, caus'ticizing a portion of the sodium carbonate thus-recovered to form a cooking liquor comprising sodium h droxide, introducing available sulfur dioxide into a hot solution that contains a substantial portion of the sodium carbonate and a substantial portion of the sodium sulfid, thus recovered, thereby removing hydrogen sulfid from the solution and converting some of the sodium content of the sodium sulfid and of the sodium carbonate into a sulfite of sodk um and forming a cookin liquor comprising "such 7 sulfite of sodium, digesting brous material with each of such cooking 1i uors, and repeating the process.

- 2. e cyclic process of producing pul from raw cellulosic fibrous material, w ic comprises digesting one lot of such fibrous material in a liquor containin a sulfite of sodium, digesting another lot 0 such fibrous material in a liquor containing sodium sulfid, se arating'aresidual liquor from resulting fibrous material from each of such digesting treatments, removing water from such residual liquors,-decomposing sodium organic compounds of both residual liquors together by means of the same furnacing treatment, thereby producing a furnace product comprising sodium carbonate and sodium sulfid, forming a cooking liquor comprising a' portion: of the recovered sodium sulfid, treating another portion of the recovered sodium carbonate and sodium sulfid to form a sulfite of sodium and forming a cooking liquor comprising such sulfite of sodium, digesting fibrous material with each of such cooking liquors, and repeating the process.

3. The cyclic process of producing pulp from raw cellulosic fibrous material, which comprises digesting one lot of such fibrous material in a liquor which is acid to litmus and contains the sulfite radicle, digesting another lot of such fibrous material in a liqco-pending applications referred to above. uor containing a reactive compound of sod1 portion of the recovered sodium carbonate um alkaline to litmus, separating a residual liquor from resulting fibrous material from each of such digesting treatments, treating the residual liquor from the first-mentioned digesting treatment by means of an alkaline sodium compound derived from the secondmentioned digesting treatment, removing water from the treated residual liquor, decomposing organic matter thereof under conditions adapted to produce a furnace product comprising sodium carbonate and sodium sulfid, introducing available sulfur dioxide into a hot solution that contains-a portion of such recovered sulfid to form and remove hydrogen sulfid and to form a sulfite of. sodium, forinin a cooking liquor comprising such formed sulfite, digesting fibrous material with such cookin liquor, and employing the resulting residual liquor in repeating the process.

4. The cyclic process of producing pulp from raw cellulosic fibrous material, which comprises digesting one lot of such fibrous material in a liquor which is acid to litmus and contains a sulfite of sodium, digesting another lot of cellulosic fibrous material in a liquor containing sodium hydroxide and sodium sulfid, separating an acid residual liquor from resulting fibrous material of the first-mentioned digesting treatment, separat ing an alkaline residual liquor from resulting fibrous material of the second-mentioned digesting treatment, treating the-acid residual liquor with an alkaline sodium compound derived from the alkaline liquor, removing water from the resulting liquor, decomposing sodium organic matter thereof under conditions adapted to form a furnace product comprising sodium carbonate and sodium sulfid, adding lime to aliquor that contains some of such recovered sodium carbonate and so dium sulfid and causticizing a portion of the sodium carbonate thus recovered to form a cooking liquor comprising sodium hydroxide and sodium sulfid, introducing available sulfur dioxide into hot liquor that contains a and sodium sulfid and therebysulfiting a portion of the recovered sodium carbonate and sodium sulfid under conditions adapted to produce a cooking liquor which contains a sulfite of sodium derived in part from the sodium carbonate and in part from the so-V dium sulfid, digesting: such fibrous material by means of each of such cooking liquors, and repeating the process.

5. The process according to the preceding claim, wherein acid residual liquor. is rendered non-acid to litmus by adding thereto a regulated amountof sodium carbonate and sodium sulfid derived from the furnacing step of the process.

6. The processaccordingto claim 4, wherein a portion of the sodium carbonate and sodium sulfid of'the furnace product is treated mg sodium carbonate and sodium sulfid. 10. The method of producing pulp from in aqueous solution with available sulfur dioxide while the liquor is maintained at around the boiling point, thereby forming hydrogen sulfid and removing it from the solution and producing a sulfite of sodium that includes sodium derived from the sodium sulfid.

7. The process according to claim 4, wherein a portion of the sodium carbonate and sodium sulfid of the furnace product in aqueous solution is treated while boiling, with sulfur dioxide gas, thereby forming hydrogen sulfid and removing it from the solution andproducing a sulfite of sodium that includes sodium derived from the sodium'sulfid.

8. The process according to claim 4, wherein a portion of the sodium carbonate and sodium sulfid of the furnace product in aqueous solution is treated While boilin with sulfur dioxide as supplied as sulfururner gases, substantially free from elementary sulfur,

thereby forming hydrogen sulfid and removing it from the solution and producing a sulfite of sodium that includes sodium derived from the sodium sulfid.

9. The rocess according to claim 4, where in the so ium organic compounds from both types, of residual liquors are 'furnaced together to produce a furnace product comprisfibrous material which comprises digesting cellulosic fibrous material in a liquor containing most of its sodium content in the form of a sulfite of sodium, treating cellulosic fibrous material in a liquor that contains most of its sodium content as alkaline sulfur-free compounds comprising sodium hydroxide, separating a residual liquor resulting from each of such treatments, mixing such residual liquors in suitable proportions, m5

subjecting the mixture to a treatment adapted to recover sodium compounds thereof as sodium carbonate and sodium sulfid, such treatment including a reducing furnacing treatment, causticizing a portion of the recovered soda product and forming therefrom a liquor that contains most of its sodium content as alkaline sulfur-free compounds comprising sodium hydroxide, introducing sulfurdioxideinto a solution that contains a taining a tri-oxy-sulfur compound of sodium and forminga cookingliquor therefrom suitable for use in the first named cooking 7 ment. 7

11. The, method according to claim 10, in whichv a portion of" the recovered soda productis treated with the sulfite radical until substantially allof the sodium sulfid in such portion is converted into tri-oxy-sulfur compound of sodium and the resulting product is subjected toa' regulated oxidizing treatportionof the recovered sodium carbonate thiosulfate is converted into a sulfite of sodi- 13. The method of producing pulp from fibrous material which comprlses dlgesting cellulosic fibrous material in an acid liquor containing sulfite of sodium, treating cellulosic fibrous material in a liquor that contains' most of its sodium content in the form of alkaline sodium compounds comprising sodium sulfid, separating a residual liquor resulting from each of such digesting treatments, mixing such residual liquors in suitable proportions and subjecting the mixture to a treatment adapted to recover sodium compounds thereof as sodium carbonate and sodium. sulfid, such treatment including'a reducing furnacing treatment, causticizing' a ortion' of the recovered soda product and orming thereof a cooking liquor for use in the alkaline cooking treatment, sulfiting a portion of'the recovered soda product to convert substantially all of the sodium sulfid into tri-oxy-sulfur'compounds of sodium containing at least some thiosulfate, subjecting the resulting'product to a regulated oxidizing treatment until substantially all of the sodium thiosulfate has been converted into a sulfite of sodium and tre'atingtthe resulting product to form a cooking liquor adapted for use in the acid cooking treatment.

14. The process according to claim 13, in

which gases from the reducing furnace are oxidized to convert sulfur containing material therein into sulfur dioxide and sulfur trioxide, separating sulfur trioxide containing material from the gases and returningit to the reducing furnace and utilizing f thei sulfur dioxide .for treating sodiumcompounds recovered from the reducing furnace I in the preparation of the acid'cookingliquor, and digesting cellulosic fiber-bearing material with the cooking liquor thus produced.

The cyclic method of treating cellulosic fiber-bearing material including ligneous matter, which. comprises digesting such material with cooking liquor that contains most of its sodium content in the form of oxy-sulfur compounds comprising a sul-- fite of sodium and a thiosulfate, treating cellulosic' fiber-bearing material by means of an alkaline liquor that contains sulfur-free alkaline compounds of sodium and also contains sodium sulfid, separating a residual liquor that' includes organic matter from fibrous material resulting from each of said treatments, removing water from such residual l1quors, subjecting together sodium compounds derived from both ofsuch residual A liquorsto a furnacing treatment. under 1'6? tures'.

ducing conditions thereby forming furnace gases that carry sulfur oxides and also forming another furnace product that contains most of its sodium compounds as sodium carbonate and sodium sulfid, dissolving such recovered sodium compounds in water, separating such alkaline solution into portions, introducing into one of such portions a sufficient amount of available sulfur dioxide to convert substantially all of the sodium content of the sodium carbonate and the sodium sulfid thereof into a sulfite of sodium and a thiosulfate of sodium, digesting cellulosic fiber-bearing material including ligneous matter by means of cooking liquor containing the sulfite of sodium and the thiosulfate of sodium thus produced, and treating cellulosic fiber-bearing material with an alkaline liquor that includes sodium sulfid contained in. another of said portions and also includes an alkaline sulfur-free sodium compound, and repeating the process.

16. The further improvement'in the method of claim 15, in which the first-mentionedcooking liquor is non-acid to litmus and the amount of sodium sulfite is larger than the amount of sodium thiosulfate therein.

17. The further improvement in the method of claim 15, in which one of the said portions of the alkaline solution is treated with lime to convert sodium carbonate into sodium hydroxide, and the resulting solution that contains sodium hydroxide and sodium sulfid is used to treat cellulosic fiber-bearing material, thereby forming an alkaline residual liquor that contains organic matter derived from the fiber-bearing material.

' 18, The further improvement in the method of claim 15, in which residual liquor from the first-mentioned digesting treatment is sprayed into hot gases formed during the In testimony whereof we affix our signa- LINN BRADLEY, EDWARD P. MoKEEFE. 

